数组：
$a = array(array(a=>aa,a1=>1,a2=>1),array(a=>bb,a1=>2,a2=>2),array(a=>cc,a1=>3,a2=>3),array(a=>aa,a1=>1,a2=>1),array(a=>bb,a1=>5,a2=>5))
第一个键值相同的元素 求和 
结果
$r = array(array(a=>aa,a1=>2,a2=>2),array(a=>bb,a1=>7,a2=>7),array(a=>cc,a1=>3,a2=>3));
回复讨论(解决方案) $a = array( array(a => aa, a1 => 1, a2 => 1), array(a => bb, a1 => 2, a2 => 2), array(a => cc, a1 => 3, a2 => 3), array(a => aa, a1 => 1, a2 => 1), array(a => bb, a1 => 5, a2 => 5),);$res = array();foreach($a as $r) { if(! isset($res[$r['a']])) $res[$r['a']] = $r; else { $res[$r['a']]['a1'] += $r['a1']; $res[$r['a']]['a2'] += $r['a2']; }}print_r(array_values($res));
array( [0] => array ( [a] => aa [a1] => 2 [a2] => 2 ) [1] => array ( [a] => bb [a1] => 7 [a2] => 7 ) [2] => array ( [a] => cc [a1] => 3 [a2] => 3 ))